Recently the trend in detergent powders has been towards increased bulk density, for example, above 650 g/l, and towards production methods that do not include spray-drying. At the same time the consumer is seeking ever better cleaning performance from the use of more potent ingredients, for example, surfactants having improved oily soil detergency, some of which are mobile liquids and difficult to incorporate in particulate compositions without leading to a deterioration in flow properties and delivery and dispersion problems in the wash: these difficulties tend to be greater in higher-bulk-density powders than in conventional spray-dried lower-bulk density powders.
Another area where the consumer demands high performance is bleaching and stain removal, especially at low wash temperatures. Many bleaching ingredients are sensitive to moisture and tend to decompose on prolonged storage, and this tendency is exacerbated in high bulk density powders where components are forced into greater proximity. Bleach stability is a particular problem in powders containing zeolite which has a high content of relatively mobile water. It is also a particular problem for bleach systems based on sodium percarbonate, which is considerably less stable to moisture than are sodium perborate monohydrate or tetrahydrate.
EP 522 726A (Unilever) discloses bleaching detergent compositions having much improved sodium percarbonate stability, in which zeolite 4A has been replaced by zeolite P having a silicon to aluminium ratio not exceeding 1.33 (zeolite MAP). Zeolite MAP is described and claimed in EP 384 070A (Unilever).
Our copending application EP 533 492A filed on 24 Nov. 1992 and published on 2 Jun. 1993 describes and claims a high-performance particulate detergent composition of high bulk density that combines a number of desirable attributes. Excellent physical detergency is assured by means of a relatively high level (15-50 wt %) of a high-performance surfactant system--ethoxylated nonionic surfactant having a low (.ltoreq.6.5) degree of ethoxylation (60-100 wt % of the surfactant system) and optional primary alkyl sulphate (0-40 wt % of the surfactant system)--and a builder system based on zeolite (20-60 wt % of the composition), preferably zeolite MAP, which also gives good powder properties despite the high level of relatively mobile surfactant.
The present inventors have now discovered that these compositions, and others containing zeolite MAP, may be still further improved by the inclusion of a high-performance bleach system based on a transition metal catalyst.
The transition metal bleach catalysts, which are manganese complexes, are described and claimed in EP 458 397A, EP 458 398A and EP 509 787A (Unilever), the last-mentioned document disclosing their use in high bulk density detergent powders. The catalysts are presented in granular form for incorporation into detergent powders. However, stability problems have been found when incorporating these catalysts into detergent powders built with zeolite, especially those of high bulk density, in that the catalyst granules tend to discolour severely on storage, appearing black (and thus highly unattractive) to the consumer.
The present inventors have found that the tendency to discoloration on storage of these catalyst granules is significantly reduced if conventional zeolite A is replaced by zeolite MAP.
It has also be found that, if zeolite A is replaced by zeolite MAP, storage-stable detergent compositions of high bulk density containing the transition metal catalyst in conjunction with sodium percarbonate bleach may be formulated. This was previously impracticable because of the instability of sodium percarbonate in the presence of zeolite A. Thus the present invention makes it possible to formulate stable detergent compositions containing an extremely potent, yet environmentally favourable, bleach system which is stable on storage.
Our copending application EP 552 054A, filed on 15 Jan. 1993 and published on 21 Jun. 1993, discloses a high bulk density detergent powder containing zeolite MAP and containing sodium percarbonate having a protective coating.